The invention relates to a method for refining oils or fats which are used in a container in the heated condition for cooking an edible product therein, which refining is carried out by passing the oil or the fat through a filter. In cooking edible products in hot oil or fat, such as frying or deep-frying potato chips (French fries), croquettes, pancake rolls, etc., the problem arises that the oil becomes contaminated in a relatively short time. This contamination is dependent on the nature of the product processed in the oil and, depending on the product, consists of contamination with a varying size range and clogging-up capacity. The burning of said contamination results in the generation of smoke and the deposit on the products, while the microscopically small particles produce the typical frying smell. In the case of installations which are in operation for prolonged periods this means a very unpleasant working atmosphere for the staff, while the product to be delivered rapidly becomes bad. Furthermore, as a result of heating the oil is subject to oxidation which is promoted by the oxygen introduced along with the product to be deep-fried.
The oxidation and the microscopic product contamination are the cause of the formation of fatty acid oxidation products. Furthermore, hydrolysis occurs due to the introduction of water with the product to be deep-fried, as a result of which free fatty acids are formed.
A limit is imposed in relation to the fatty acid content by the Keuringsdienst van Waren (Food Inspection Department).
Cleaning the oil with a filter is known. However, this is either not done at the right time, viz. after the oil has been used, or continuously but to an inadequate extent and in a manner which results in the oil deteriorating, for example, as a result of the introduction of oxygen. Little is thereby achieved. Although coarse particles can be separated off in said manner, the very fine particles and the fatty acids or fatty acid oxidation products, or the water, remain present in the oil.